BGA SOLDER BALL to SURFACE PAD size relationship

Robert, Here's my recommendation's: Solder paste opening on screen should equal the solder mask opening on board. Stencil thickness at .008" but this should not be your main concern as stencil thickness should be determined by the fine pitch that are located on the board ( unless you have step down's ) That's just my opinion, I could be wrong!

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I usuallly like to have the pad size the same size as the ball up to +2mil, the pcb solder mask opening to be +4 mil from the pad size (I have found this to aid in Xray inspection for opens since you can see the little tail of the solder wicking up the trace to the mask, I also like to downsize the stencil opening to pad size -2 mil. I reduce the paste volume to help in reducing void formation (less metal) We use 6 mil stencils for everything because of fine pitch components.

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Robert: Ah, opinions are like mothers, everyone has one. Here's mine:

1 Goto the Altera site, get a copy of "AN 114," follow it. Generally, manufacturers are closer to the requirements of their components than others are. 2 Metal showing on the board pad SB the same size and shape as the metal showing on the BGA interposer. That'll give you balanced forces between the top and the bottom of the ball. No "torquing" for you laddie. 3 Type of mask / ball interface (SMD versus NSMD) SB the same on the BGA and the board. That'll give you balanced forces between the top and the bottom of the ball. 4 With a 0.006 inch thick stencil, assuming you have 0.025 inch pitch or less components on your board as well as the BGA, the BGA aperture SB the same size and shape as the metal showing on the pad.

Good luck and happy opinuating to all,

Dave F

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